Road pavement typically includes a granular base and a bound surface layer made of asphalt or concrete. The interface between the surface layer and the granular base is considered to be one of the most important pavement interfaces. Horizontal (radial) strains at that level are considered to be directly related to the fatigue performance of the pavement structure.
Horizontal strains at the bottom of the pavement surface layer have been measured for several decades to support pavement mechanistic analysis and design. Two types of strain gauges have been used for that purpose. The first approach consist in placing an “H”-shaped gauge on top of the granular base prior to building of the surface layer (typically asphalt concrete or Portland cement concrete). The “H” shape of the proof-body allows proper anchoring of the gauge in the surfacing layer material for reliable measurements of horizontal strains. However, high mechanical and thermal stresses are imposed to the gauge by the compaction of the surface layer while the surfacing layer material is still hot. These stresses often result in gauge damage, displacement and misalignment.
The increasing need to investigate the mechanical response and performance of existing pavements has led to the development of another approach to strain measurements in existing pavement bound layers. The approach consist of coring existing pavements in order to reprocess a core of the surface layer which is glued back in its original position after a strain sensor is affixed to the bottom of the core. Several questions regarding the ability of the core to effectively transmit stresses of the surrounding surface layer to the sensor affixed to its base remain unanswered.